To investigate the determinants of endothelial cell damage in hypertensive elderly patients, we measured the plasma von Willebrand factor (vWF) levels by a recently developed enzyme-linked immunosorbent assay using monoclonal antibody for the functional epitope. Plasma vWF level was markedly increased in the elderly normotensive subjects (n = 42) than in younger normotensive subjects (n = 39) (127 vs 88%, p < .0001), and was further increased in elderly hypertensive subjects (n = 68) (148%, p < .05 vs elderly normotensives). The vWF level was positively correlated with body mass index in younger normotensive subjects (r = 0.41, p < .01), with systolic blood pressure (BP) in elderly normotensive subjects (r = 0.41, p < .01), and with age (r = 0.44, p < .001) and fibrinogen level (r = 0.37, p < .01) in elderly hypertensive subjects. In elderly hypertensive subjects (n = 150), vWF level had a stronger positive correlation with 24-hr systolic BP measured (r = 0.41, p < .0001) by ambulatory BP monitoring than with clinic systolic BP (r = 0.33, p < .0001). In conclusion, in hypertensive elderly patients, endothelial cell damage increases with systolic BP and fibrinogen levels, indicating a prethrombotic condition.